Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755505AbZCEHhs (ORCPT ); Thu, 5 Mar 2009 02:37:48 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751956AbZCEHhi (ORCPT ); Thu, 5 Mar 2009 02:37:38 -0500 Received: from casper.infradead.org ([85.118.1.10]:45517 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750728AbZCEHhi (ORCPT ); Thu, 5 Mar 2009 02:37:38 -0500 Subject: Re: [Bug #12809] iozone regression with 2.6.29-rc6 From: Peter Zijlstra To: "Zhang, Yanmin" Cc: Wu Fengguang , "Lin, Ming M" , Nick Piggin , Andrew Morton , lkml In-Reply-To: <1236219189.2567.123.camel@ymzhang> References: <20090305010920.GB11575@localhost> <1236218012.2567.115.camel@ymzhang> <20090305020408.GA26425@localhost> <1236219189.2567.123.camel@ymzhang> Content-Type: text/plain Date: Thu, 05 Mar 2009 08:37:29 +0100 Message-Id: <1236238649.5330.10132.camel@laptop> Mime-Version: 1.0 X-Mailer: Evolution 2.25.91 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1335 Lines: 31 (list restored) On Thu, 2009-03-05 at 10:13 +0800, Zhang, Yanmin wrote: > My idea: > 1) When the main thread traps into kernel and find need to write back pages; it just starts > write back, but it needn't change timestamp (???or something like that) on writeback; and start > pdflush; > 2) Later on pdflush could pick up the file to write back for other pages on the same file; > 3) The target is to let pdflush to writeback pages and main testing thread continues on its own > work, so we can benefit from SMP. No! This is not about parallelism, this is about making sure there is a limited number of dirty pages, that means the tasks generating dirty pages will _have_ to wait. You simply cannot delegate that. Furthermore, the task throttling explicitly wants to throttle the task that generates all those dirty pages more than other tasks. So pushing the throttle out to pdflush will destroy the whole scheme. The reason we want to make the heavy dirtier throttle sooner is that other tasks, who only occasionally dirty a page, don't get caught in the massive throttle latency. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/